Dan,
That issue was fixed so many versions back that I can not remember what I did to fix it. It would take me to much time to go back and try to find what the issue was and the fix for it. Based on the readme.txt this issue was fixed in version 2.5.0.6
Version 2.5.0.6 - 12/21/2011
* Fixed issue where in some circumstances the Fixed Data Grid could
extend past the applications width.